Many halogenated organic compounds soluble in fatty materials, exhibit high chemical stability and are resistant to biodegradation. Consequently, there is an increase of their concentration in the food chain. Several studies have clearly shown the intrinsic toxicity of these compounds and also their potential toxicity during a thermal treatment. When heated at a temperature from 300.degree. to 900.degree. C. in the presence of air, PCB produce dioxins and benzofurans some isomers of which are still more toxic.
For these reasons, several institutions for environmental protection have promulgated strict regulations concerning the use of commercial compositions containing halogenated organic compounds. These regulations impose strict controls on industrial oils which have a high likelihood of PCB contamination. These fluids are classified according to their contamination level. The U.S. Environmental Protection Agency has promulgated rules under which PCB-containing oils can be broken down into the following categories:
PCB-free oils: oils containing less than 50 ppm PCB; PA1 PCB-contaminated oils: oils containing 50-500 ppm PCB; PA1 PCB-oils: oils containing more than 500 ppm PCB. PA1 PCB have been largely used as dielectric fluids in transformers and condensers, in lubricating oils, heat-transfer fluids, and also as additives in glues, paints, asphalts, synthetic resins, fibers, and coatings, etc. However, despite this wide range of application, the electrical industry is the main source of contamination by PCB.
Oils containing more than 50 ppm PCB may be eliminated by burning in high temperature incinerators, but the latter must meet several strict conditions. Therefore, the treatment cost is high. Moreover, the valuable oil is completely destroyed and lost.
Physical methods, such as distillation, extraction by selective solvent and adsorption by charcoal, may also be used for the elimination of PCB from mineral oils. However, PCB are not destroyed by these methods. The problem is not how to eliminate PCB from oils, but how to destroy these PCB.
It is, therefore, important to develop a method for the chemical destruction of halogenated organic compounds by cleavage of the carbon-halogen bond.
Several chemical methods have already been suggested for the decontamination of mineral oils containing polyhalogenated aromatic compounds. The PCB content of an oil may be decreased by treating said oil with solid sodium or with a dispersion of sodium in a liquid hydrocarbon. However, the yields are low, even at high temperatures where the intrinsic properties of the treated oil are greatly damaged. Another process consists of using a sodium-naphthalene or sodium-biphenyl complex in a suitable solvent, such as diethylether. This process has two main drawbacks: first, the handling of sodium is dangerous and, second, it is difficult to separate the oil and the reagents after the treatment step.
It has also been suggested to employ a technique which consists of contacting the mineral oil with an alkali metal glycolate which has been previously prepared from a polyglycol and an alkali metal or its hydroxide. The reaction with the oil must be carried out in the absence of oxygen and at an elevated temperature (about 130.degree. C.) in order to achieve good yields. However, the oil is degraded at this temperature (U.S. Pat. Nos. 4,337,368; 4,353,793; 4,400,552 and 4,460,797; European Patent Application No. 60089).
Other processes for the decontamination of mineral oils containing halogenated aromatic compounds consist of using alkali alkoxides in the presence of a solvent, such as a sulphoxide. But, once more, the reaction temperatures are elevated. Moreover, an additional step is required to separate the solvent and the treated oil.
According to another process, the mineral oil is treated with a reagent mixture prepared from a polyether, a free-radical generating compound, such as a peroxide, and a weak base (European Patent Application 118858). A preliminary step is required to prepare the reagent mixture. Furthermore, the decontamination reaction must be carried out with the aid of microwaves to reduce the reaction time.
There is thus a need in the art for a process for the chemical decomposition of halogenated organic compounds which achieves high yields using a reagent which does not require a preliminary preparation step.